Symfony Console OutputFormatter replaces "<<" with "\"

On a console command, with the standard OutputInterface instance
`$output->writeln("<<");`
actually outputs:

```
\
```

expected:

```
<<
```

The cause is the implementation of the method format in OutputFormatter, see line 177:

``` php
if (false !== strpos($output, '<<')) {
    return strtr($output, array('\\<' => '<', '<<' => '\\'));
}
```

Symfony version: 3.0.4
